Process of hydrating phosphoric anhydride



Jan. 8, 1929. 1,698,484- E URBAlN PROCESS OF'HYDRATING PHOSPHORIC ANHYDRIDE Filed April 21, 1927 COKE 50x HEAT EXOHHNGER MQ (MM ATTORNEYS CONCENTRATING TOWER EDOUABD 'URZBAIN, OF PARIS, FRANCE, ASSIGNOR TO URBAIN CORPORATION, A COR- PORATION OF DELAWARE.

rnocnss'or HYDRATING rnosrrroiuo ANHYDRIDE.

Application filed April 21, 1927, Serial No. 185,425, and in France April 21, 1926.

The present invention relates to a process of hydrating phosphoric anhydride produced by the combustion of phosphorus, and is con ducted .in such a way that the heat of com- 6 bustion is used to concentrate the acid solution produced. r

The process can best be understoodby reference to the accompanying drawings in which a diagrammatic arrangement of appa- 10 ratus is shown. I

In these drawings numeral 10 designates retorts adapted to produce phosphorus vapor, asfor example, by heating material comprising the P0 radical in the presence of carbon. The phosphorus vapor and other gases present pass into a chamber 11 in which the phosphorus is burned. Air is admitted through a port 12 controlled by a damper 14. The temperature in the chamber 11 can be controlled by the amount of air admitted. I have found that satisfactory results are obtained when the temperature is maintained between 900 and 1100 C. Anynitrogen and excess of oxygen present will be heated up to this temperature by the combustion.

The gases resulting from this combustion are sent into the base of a Gaillard concentrating tower 16 where they meet the solution of phosphoric acid to be concentrated. This an acid (which may have a specific gravity of from 20 to 22 B. when it enters the tower) is forced into the top of the tower by the acid lift 17 and drops down through the tower in the form of a spray. Upon meeting the hot gases there is a heat exchange, and the solution of phosphoric acid is concentrated so that at the bottom of the tower one can draw ofi phosphoric acid of a strength of about50 B.

A pipe 18 is provided for this purpose. The

gases of combustion as they rise in the tower 16 pick up from the phosphoric acid solution the necessary water vaponfor hydrating the phosphoric anhydride to form phosphoric acid, which is later returned to the tower.

The gas comes out of the top of the tower through the pipe 20 at a temperature of between 200 and 280 C. It then passes to heat exchanger 22 made up of a series of tubes submerged in a dilute solution of phosphoric acid. This dilute solution of phosphoric acid (originally having a concentration of from about 17 to 20 B.) flows into the heat exchanger 22 from coke boxes 24. The acid from the heat exchanger 22 is sent through the concentrating tower as has already been explained. It is important in arranging the heat exchanger, thatthe gases should not be cooled below about 120 C. and certainly should not be allowed to drop below 100 C. as otherwise excessive condensation will ensue.

The mixture of phosphoric anhydride and steam pass into the coke boxes 24 where the coke (which may be in pieces the size of a pea) serves as a catalyst to assist in the hydration and condensation of the acid. The temperature will tend to rise during this reaction but may be kept down by water admitted through pipe 26. Fixed gases can be vented off through the pipe 28. The phosphoric acid formed will pass into the heat exchanger 22 through the pipe 30.

1 It will be noted that in this process the water is continually cycled and the only water which is drawn out of the apparatus is that which combines with the phosphoric anhydride. Water introduced serves to cool the coke boxes. Therefore all the heat units are utilizedin a most efiicient manner.

What I claim is:

1. The process of converting phosphorus into phosphoric acid which comprises the steps of burning phosphorus, contacting the gases with dilute phosphoric acid previously formed in the cycle of operations, whereby the acid is concentrated and the gases are mixed with steam, passing the mixture of gases and steam through a heat exchanger whereby additional heat is given up by the gases to previously formed phosphoric acid, converting the mixture of gases and steam into liquid phosphoric acid in the presence of a catalyst and concentrating the resulting acid by the counter-current flow of additional quantities of gas as already described.

2. A process as defined in claim 1, in which the water Withdrawn in the phosphoric acid isadded at the time of hydration whereby the catalyst is kept cool.

I EDOUARD URBAIN v 

